When dimming the luminous intensity of a light-emitting means, for example of a conventional incandescent lamp, a redshift can often be perceived and be desirable. The redshift is formed owing to a change in the temperature of a metallic wire through which electric current is flowing from a high temperature value to a low temperature value. In the case of incandescent lamps, this is technically absolutely the case.
In the case of light-emitting diodes, for example white light-emitting diodes, a constantly high color temperature can have an irritating effect at a low luminous intensity or in the case of low levels of dimming. In the case of light-emitting diodes (LEDs), variable color temperatures are conventionally realized with different, sometimes very technically complex and cost-intensive mixing methods.
In a conventional method, the color locus of a light-emitting diode can be set for example, by means of the current intensity through the LED and/or the ON time of the LED (pulse width).
In a further conventional method, the color locus of an LED light can be set, for example, by means of different LED chains, wherein the LED chains can have one or more identical or different LED chips. In this case, the light from at least one first LED chain and one second LED chain of different color temperature is mixed in a diffuser.
The first LED chain has a higher color temperature than the second LED chain. For dimming of the LED light, the current through the first LED chain is reduced, while at the same time the current through the second LED chain is increased. In the case of intense dimming, the current through the LED chain with a low color temperature is then reduced again, i.e. the current through both LED chains is low.
The maximum current intensity through the LED chains is not present at the same time, i.e. the LED light could emit light with a higher light intensity than is actually taking place. Owing to the nature of the actuation of the LED chains, the possibility of the higher luminous intensity is not utilized, however, as a result of which the LED chips in the LED chains are not used optimally.
Furthermore, at least two LED chains, one driver per LED chain and one control unit for the drivers is required for this method of variable-color LED light.
As a result, dimmable, variable-color LED lights can be more cost-intensive than LED lights without the possibility of color variation.